Ferroelastic crystals and their nonlinear elastic properties observed in frequency range from gigahertz to milihertz

Abstract

The experiments reported in this article have been performed to unify the results of earlier and recent determinations of parameters describing the elastic properties of Rb₄LiH₃(SO₄)₄, LiCsSO₄ (LCS) and KH₂PO₄ crystals measured by different experimental methods. The above crystals undergo a second-order phase transition, incommensurate phase transition (PT) and a first-order but close to second-order phase transition, respectively. To investigate the elastic properties of the crystals in the frequency range from 10⁻¹ to 10¹⁰ Hz, five experimental methods were applied: dynamic mechanical analysis, piezoelectric resonance, composite oscillator bar, ultrasonic wave propagation and Brillouin light scattering. The results of the experiments allowed identification of the processes contributing to the elastic response of the crystals investigated. Moreover, for the LCS crystal a model of the incommensurate PT was presented.

Keywords:

• ferroelastic
• phase transitions
• incommensurate
• Brillouin
• DMA
• composite oscillator bar
• piezoeffect
• ultrasound
• unification

Acknowledgements

The author thanks Prof. B. Mroz, Prof. A. Lehman–Szweykowska, Prof. M. Kurzyński, Prof. Z. Tylczynski, Prof. S. Mielcarek and Dr P. Biskupski for the inspiration and for fruitful discussions. This work was supported by the Ministry of Education and Science, Grant No. 1BO3B066030.